Vehicular theft preventing device having a setting switch for setting the theft preventing device in an alarm unit is proposed, for example, in Japanese Patent Application Laid-Open Publication No. HEI-10-305789 (JP 10-305789 A). In the vehicular theft preventing device disclosed in JP 10-305789 A, a theft preventing circuit includes an electronic theft preventing key, an inclination angle sensor, a secret setting switch, etc. The theft preventing circuit is activated in response to turning-on of the secret setting switch.
However, with the vehicular theft preventing device disclosed in JP 10-305789 A, where the separate, secret setting switch dedicated to the vehicle is provided, it is necessary to secure a space for installing wiring for connection to the setting switch, and thus, it is considerably difficult to freely position the setting switch and the positioning of the setting switch would entail great limitations. In addition, the setting switch must be provided at such a position of the vehicle body that it can not be readily found by third persons. Positioning the setting switch at a hard-to-find position would influence the overall layout of various components on the vehicle body and thus undesirably lower the design freedom of the vehicle.